“I've always wondered why marketers care so much about the ‘all-important’ male 21-to-35 demographic. What is so important about that group? As a male in my mid-40s I spend a lot more money than I did back then. What am I missing?”

Short answer is -- it’s actually the opposite sex who marketers spend the most to reach. After all, women are responsible for most consumer spending decisions, especially in families.

But, Brock Groth is also right. Younger men are an 'all-important' marketing target for key consumer categories and brands—everything from late-night TV, to alcoholic beverages, athletic footwear, sports entertainment, and pickup trucks.

Michael Jordan -- the old, and the young -- battle it out in a one-on-one, for Gatorade.

There’s the battle for ratings on late-night TV:

It’s an insult-a-minute . . . when it’s not a frat-boy comedy-fest featuring various bodily fluids.

And then there’s the attraction of pretty much anything suggesting sex.

Media analyst Jack Myers is author of the forthcoming book 'The Future of Men: End of the Age of Dominant Males,' and he says: “Beer commercials continue to be appealing to men as completely male-focused misogynists who have women around them at bars or sporting events only to serve their needs. Or, men are idiots, they’re the buffoons who aren’t even capable of knowing which analgesic they should take.”

Still, retail-industry expert Patty Edwards at U.S. Bank Wealth Management says it pays to try to grab them now, before they get older -- and likely more mature.

“That 18-to-34-year-old male demographic are either newly married or not yet married,” says Edwards. “In a lot of cases they’re living at home or living with friends. They have a lot of disposable income.”

The so-called Yummies -- “young urban males” -- are getting a lot of attention after a report from HSBC pegged them as the most promising market for luxury goods—things like $1,000-plus briefcases, clothing, jewelry, cosmetics, for brands like Coach, Burberry, Michael Kors and Prada.

But Edwards says even young men on a modest salary will spend: “A bottle of aftershave, if it gets you the girl, it’s worth every penny.”

Government consumer spending data show that young men (up to age 34) spend more than young women overall, and also in key categories for marketers—new cars and trucks, alcohol, entertainment. For booze and eating out, they even spend more than older men, who have significantly more disposable income.

Patty Edwards says once women enter the picture, men make fewer consumer purchasing decisions. “It’s actually women who control the majority of spending, even over this demographic,” says Edwards. “And it’s because no guy does much of anything without permission from his wife or girlfriend.”

So why then is the 18-to-34-year-old male still such a key demographic for marketers? Because his wallet’s full. Unlike the typical female consumer, he’s more likely to spend what he wants, without thinking too much about what he needs. So if you’re Bud, or Jeep, or Nike, you want to get him hooked on your brand, before someone with more grown-up spending habits—likely a woman—starts putting him right.